The present invention relates to a process for the extremely rapid inscription of photo-addressable substrates, substrates prepared for this process, and the use of such substrates in information technology. The invention also relates to photo-addressable side-group polymers in which a high double refraction can be induced by irradiation, so that they are suitable for storing optically available information or for producing passive or optically switchable components.
Photo-addressable polymers are known (Polymers as Electrooptical and Photooptical Active Media, V. P. Shibaev (Editor), Springer Verlag, New York 1995). Particularly suitable for this purpose are side-group polymers, of which the group of copolymers is distinguished by a very wide range of possible variations of the properties. Their particular feature is that their optical properties such as absorption, emission, reflection, double refraction and scattering can be reversibly altered by light induction. Such polymers have a special branched structure: side groups that can absorb electromagnetic radiation and that are joined by parts of molecules acting as xe2x80x9cspacersxe2x80x9d are located on a linear backbone. Examples of this type are the side-group polymers containing azobenzene groups according to U.S. Pat. No. 5,173,381. These substances are characterised by the ability to exhibit double refraction in a specific direction when irradiated with polarised light. The inscribed double refraction patterns can be rendered visible in polarised light.
It is also known that a locally restricted double refraction whose preferred axis moves with the rotation of the direction of polarisation can be inscribed at an arbitrary position in layers of these polymers using polarised light (K. Anderle, R. Birenheide, M. Eich, J. H. Wendorff, Makromol. Chem., Rapid Commun. 10, 477-483 (1989), J. Stumpe, et al., 20. Freiburger Arbeitstagung Flxc3xcssigkristalle 1991). These processes are slow. Although in some cases the beginning of anisotropic behaviour can be detected already after a few seconds"" exposure time, as a rule minutes and even hours are necessary in order for the effect to reach its achievable maximum. In this connection the magnitude of the effect is roughly proportional to the time employed. It is a particular feature of optical addressing that the optic axis of the inscribed double refraction is vertical to that of the inscribing polarised light. The simple possibility of being able optically to extinguish inscribed information by rotating the direction of polarisation of the inscribing light is based on this property. Inscription and extinction occur equally rapidly in this case; they are identical processes up to the direction of polarisation of the employed light. This is in contrast to the process of thermal extinction by heating the layer above the glass transition temperature of the polymer, in which all information is extinguished at once.
In data representation, storage and processing, two fundamentally different routes are followed, which may be termed serial and analog. In the analog route all data and information are simultaneously collected and converted. A typical example of this is photography using a silver halide film as an analog recording medium. This case involves exposure of a layer of photo-addressable polymers with polarised light through a master pattern. Since all image points are developed simultaneously, the inscription (development) time is seldom critical in these processes. With serial processes however the items of information are called up in succession. In the case of objects with a very high information density, for example images, potentially very large numbers of these image points have to be inscribed in succession, and the development time is thus the summation of the development times of the individual image points. For this reason a high inscription rate while maintaining a sufficient stability of both the initial state of the non-inscribed regions as well as of the final state of the inscribed regions is important. In both processes the accurate reproduction of gradations of differences in brightness (grey Stages) of the master pattern is also extremely important. Hitherto it has not been possible to solve in a technically satisfactory manner the problem of high inscription rates by the optical route, since in addition to the information transmission rate, further boundary conditions are essential. Such boundary conditions include in particular the stability, the extinguishability, and the ability to distinguish degrees of greyness. There are fundamental reasons for this.
As a general rule, only systems in which no mass but only fields or vectors are changed, can react extremely rapidly to control commands. If a mass is moved, for example in rearrangement processes or chemical reactions, the reaction is orders of magnitude slower and is governed also by the viscosity of the medium. For example, the switching time of the low-viscosity nematic rotational cells is at most in the region of msec, whereas a side-group copolymer takes minutes, often many hours, in order to reach the maximum achievable double refraction.
If the reversibility of the inscribed changes is dispensed with, then the energy density can be chosen arbitrarily and in the limiting case the substrate may be locally destroyed. Such materials are described for example by G. Kxc3xa4mpf in Kirk-Othmer, Encyclopaedia of Chemical Technology, 4th ed., 14, 277-338 (1995). This process, many variants of which are described in the literature, has some disadvantages however. The most important of these is that the process involves a considerable attack on the structure of the substrate, and the hole that is formed is basically unstable. In addition there is always the problem of the vaporised material, which may be deposited anywhere in the apparatus or on the storage medium, and finally very high laser energy densities are required, as a rule greater than 107 mJ/m2.
Since the preservation of the substrate is at the same time the necessary condition for its re-inscribability, the light intensity cannot be increased arbitrarily; instead, the intensity must remain below the decomposition threshold. The stability of the material thus defines the upper limit of the energy density. The smallest amount of energy that is necessary in order to produce a detectable and stable change in the layer has been measured by Coles (in a polysiloxane) as 4xc3x97106 mJ/m2 (C.B. McArdle in Side Chain Liquid Crystal Polymers, Editor. C. B. McArdle, Blackie Publishers, Glasgow 1989, p. 374). Assuming that the minimum energy for polymeric substrates is of the same order of magnitude, it follows, if one wishes to treat the substrate gently, that the side-group polymers can only be inscribed slowly (since the minimum energy is already very close to the destruction energy), and accordingly such polymers are unsuitable for serial storage in real time. This principal disadvantage has up to now prevented the technical use of such polymers, and it is the object of the present invention to alleviate this defect.
We have now surprisingly found that extremely rapidly addressable storage media can be produced from the polymers that are slowly photo-addressable per se if the substrates are irradiated over a large area with a light source suitable for conventional inscription, so that an optical anisotropy is produced. Optical anisotropy means that the rate of propagation of the light in the plane of the layer is dependent on the direction. This produces direction-dependent refraction, so-called double refraction. If the suitably prepared substrates are irradiated for a short time with appropriately intensive light, the double refraction is varied extremely rapidly and permanently, i.e. is reduced or completely extinguished. The degree of residual double refraction can be adjusted according to the light intensity.
Two optical processes are thus involved, which differ in their action:
In a generative first process the layer must first of all become anisotropically double refractive over its area. The double refraction (optical anistropy) is conventionally expressed as the difference xcex94n of the maximum, direction-dependent refractive index n at a specific wavelength.
Any light source for polarised light, for example an incandescent lamp with a connected polariser foil or preferably a laser, is suitable for generating the large-area anisotropic double refraction. The required time depends substantially only on the power density of the light source, in which connection no lower limit for this is known at present. The upper limit of the power density of the light source is determined by the destruction threshold of the material, which depends on the material itself and is in the range from 107 to 108 mW/m2. The material may be addressed over a large area in a structureless manner or selectively, for example through a mask, though structureless addressing is preferred, especially addressing that covers the whole area of the substrate. The optical anisotropy xcex94n of the first process that is necessary for the purposes of the invention may be very small; the only precondition is that it is still measurable. Preferably the anistropy xcex94n produced in the first process is at least 0.001, in particular at least 0.005; it is preferably at most 0.95, in particular at most 0.8.
The second optical process relates to the use of the substrates prepared in the first optical process and comprises addressing with light of very short duration the material made anisotropically double refractive. The inscribing light has a further quality however: it may be polarised or unpolarised. Polarised light is preferred whose axis lies parallel to that of the substrate. The energy density should as a rule be 103 to 107, preferably 105 to 6xc3x97106 mJ/m2. xe2x80x9cShort timexe2x80x9d means that the action of the light may last for 10xe2x88x9215 to 10xe2x88x923, preferably 10xe2x88x9210 to 10xe2x88x925 sec. The light source must be correspondingly quick, which means that laser light sources are preferred. With this method sequential inscription rates of up to 100 MHz, preferably 5 to 50 MHz, are possible. The sequential addressing means that although the absorption of the photon in the material takes place extremely rapidly, there is still sufficient time for a dark reaction.
Extinction may take place over a large area, with the result that an unstructured pattern is produced. Patterns with structures that have a diameter of 10 nm to 20 xcexcm, in particular 10 nm to 1 xcexcm, in the direction of their smallest extension are however preferred.
The inscribed information is stable, i.e. after the light source is switched off a storable double refraction pattern is obtained that can be read with the aid of polarised light. The change in brightness is proportional to the action of the light. The material is capable of grey gradations. The inscribed information is reversible, i.e. the information can be re-extinguished and then re-inscribed.
The invention accordingly provides the use of flat materials with an optical anisotropy xcex94n of 0.001 to 0.95 produced from photo-addressable polymers, for storing optically available information by partially selectively varying the optical anisotropy. A further subject of the invention is a process for storing patterns in the flat materials to be used according to the invention, by irradiating with light of an energy density of 103 to 107 mJ/m2 for a duration of 10xe2x88x923 to 10xe2x88x9215 sec.
The term xe2x80x9coptically anisotropicxe2x80x9d within the context of the invention means a difference xcex94n of the maximum, direction-dependent refractive index of at least 0.001 at a wavelength that is 30 nm shorter than the point at which the absorption in the long wavelength edge of the longest wavelength absorption maximum is still 1% (absorption maximum=100%). Anisotropy values that are high as possible are desired, since they permit good results even at very low layer thicknesses. Preferred values of xcex94n are in the range from 0.05 to 0.95, in particular from 0.1 to 0.8.
The invention further provides polymers in which an optical anisotropy can be produced by pretreatment, and which can be varied by exposure for a period of 10xe2x88x923 to 10xe2x88x9215 sec.
Suitable polymers for the production of the photo-addressable substrates are those in which a directed double refraction can be inscribed (Polymers as Electrooptical and Photooptical Active Media, V. P. Shibaev (Editor), Springer Verlag, New York 1995, Natansohn et al., Chem. Mater. 1993, 403-411). In particular these are side-group polymers, preference being given to the copolymers. Preferred examples of such copolymers are described for example in DE-OS 43 10 368 and 44 34 966. They preferably contain a poly(meth)acrylate main chain acting as backbone, with repeating units 
wherein R denotes hydrogen or methyl, the dots denote the coupling of the further units of the main chain, and the side chain is coupled to the carbonyl group.
The invention furthermore provides polymers with side chains having the structures described hereinafter.
The side chains branching from the main chain may correspond to the formulae
xe2x80x94S1xe2x80x94T1xe2x80x94Q1xe2x80x94Axe2x80x83xe2x80x83(I)
and
xe2x80x94S2xe2x80x94T2xe2x80x94Q2xe2x80x94Mxe2x80x83xe2x80x83(IIa)
wherein
S1, S2 denote independently of one another the atoms O, S or the radical NR1,
R1 denotes hydrogen or C1-C4 alkyl,
T1, T2 denote independently of one another the radical (CH2)n, which may optionally be interrupted by xe2x80x94Oxe2x80x94, xe2x80x94NR1xe2x80x94 or xe2x80x94OSiR12Oxe2x80x94, and/or may be substituted by methyl or ethyl,
n denotes the numbers 2, 3 or 4,
Q1, Q2 denote a divalent radical,
A denotes a unit that can adsorb electromagnetic radiation, and
M denotes a polarisable aromatic group containing at least 12 xcfx80-electrons.
Particularly preferred are polymers in which
Q1, Q2 denote independently of one another Z1, Z2 or the group xe2x80x94Z1xe2x80x94Xxe2x80x94Z2xe2x80x94, wherein Z1, Z2 denote independently of one another the groups xe2x80x94Sxe2x80x94, xe2x80x94SO2, xe2x80x94Oxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CONR1xe2x80x94, xe2x80x94NR1COxe2x80x94, xe2x80x94NR1xe2x80x94, xe2x80x94Nxe2x95x90Nxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Nxe2x95x90CHxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94 or the group xe2x80x94(CH2)m where m=1 or 2, and
X denotes a 5-membered or 6-membered cycloaliphatic, aromatic or heterocyclic ring, and in the case where Z1=xe2x80x94COOxe2x80x94 or xe2x80x94CONR1xe2x80x94 denotes a direct bond or the group xe2x80x94(CHxe2x95x90CH)mxe2x80x94,
m having the aforementioned meaning,
A denotes the radical of a monoazo dye that absorbs in the wavelength range between 650 and 340 nm, and
M denotes the radical of a polarised and further polarisable aromatic, linearly structured system with at least 12 xcfx80-electrons.
Preferred radicals A correspond to the formula 
wherein
R2 to R7 independently of one another denote hydrogen, hydroxyl, halogen, nitro, cyano, C1-C4 alkyl, C1-C4 alkoxy, CF3, CCl3, CBr3, SO2CF3, C1-C6 alkysulfonyl, phenylsuphonyl, C1-C6 alkylaminosulfonyl, phenylaminosulfonyl, aminocarbonyl, C1-C6 alkylaminocarbonyl, phenylaminocarbonyl or COOR1.
Preferred radicals M correspond to the formula 
wherein
R8 to R13 independently of one another denote hydrogen, hydroxyl, halogen, nitro, cyano, C1-C4 alkyl, C1-C4 alkoxy, CF3, CCl3, CBr3, SO2CF3, C1-C6 alkysulfonyl, phenylsuphonyl, C1-C6 alkylaminosulfonyl, phenylaminosulfonyl, aminocarbonyl, C1-C6 alkylaminocarbonyl, phenylaminocarbonyl or COOR1 and
Y denotes xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CONHxe2x80x94, xe2x80x94NHCOxe2x80x94, xe2x80x94Oxe2x80x94, xe2x80x94NHxe2x80x94, xe2x80x94N(CH3)xe2x80x94 or a single bond.
Preferred are amorphous polymers, i.e. polymers that do not form macroscopically detectable liquid crystal phases. xe2x80x9cAmorphousxe2x80x9d denotes an optically isotropic state. Such polymers do not scatter visible light nor do they contain a double bond.
The compounds may be prepared in a manner known per se by copolymerising mesogene-containing and dye-containing monomers, by a polymer-type reaction or by polycondensation. Free-radical copolymerisation of the monomers is preferred, i.e. of the monomers with mesogenic groups on the one hand and dye-containing groups on the other hand, in suitable solvents, for example aromatic hydrocarbons such as toluene or xylene, aromatic halogenated hydrocarbons such as chlorobenzene, ethers such as tetrahydrofuran and dioxane, ketones such as acetone and cyclohexanone and/or amides such as dimethyl formamide, in the presence of conventional radical-donating polymerisation initiators, for example azodiisobutyronitrile or benzoyl peroxide, at elevated temperatures, for example at 30 to 130xc2x0 C., preferably at 40 to 70xc2x0 C., and as far as possible under the exclusion of moisture and air. Purification can be carried out by precipitating or dissolving and reprecipitating the resultant side-chain copolymers from their solutions, for example with methanol.
Whereas the groups that can absorb electromagnetic radiation as a rule absorb in the wavelength range of visible light, the mesogenic groups of side-group polymers that are known up to now have an absorption maximum at a substantially shorter wavelength, preferably at wavelengths of around 33000 cmxe2x88x921; the achievable double refraction changes are less than 0.1. The hitherto described processes for storing information by double refraction changes have usually been described as reversible, i.e. with a temperature rise produced by light or heat the stored information can be extinguished again; the use of light may offer the advantage of a locally restricted extinguishability, which is why this variant is sometimes preferred. The principal method of extinction by adding energy in the form of heat of course at the same time runs the risk of insufficient heat stability of the inscribed information; indeed, this is a disadvantage of the previously known prior art. Many compounds of this type thus have the disadvantage that the inscribed double refractions are not heatstable; at elevated temperatures, especially on approaching the glass transition temperature, the double refraction becomes weaker and finally disappears completely. Advantageous information carriers are accordingly those in which the stability of the inscribed information is as temperature insensitive as possible.
It has now been found that superior side-chain polymers are formed if the side chains are chosen so that their absorption maxima are at a specified distance from one another. In these new polymers information that is extremely heat stable can be inscribed using light.
The invention accordingly also provides polymers that carry side chains of different types on a main chain acting as a backbone, both of which can adsorb electromagnetic radiation (for one type at least, preferably of the wavelength of visible light), provided that the absorption maxima of the different side chains are at a distance of at least 200, preferably at least 500, and most 10,000, preferably at at most 9,000 cm1, from one another.
Preferred polymers according to the invention carry on a main chain acting as a backbone covalently bonded side groups branching therefrom and having the formulae
xe2x80x94S1xe2x80x94T1xe2x80x94Q1xe2x80x94Axe2x80x83xe2x80x83(I)
and
xe2x80x94S2xe2x80x94T2xe2x80x94Q2xe2x80x94Pxe2x80x83xe2x80x83(IIb)
wherein
S1, S2 denote independently of one another oxygen, sulfur or NR1,
R1 denotes hydrogen or C1-C4 alkyl,
T1, T2 denote independently of one another the radical (CH2)n, which may optionally be interrupted by xe2x80x94Oxe2x80x94, xe2x80x94NR1xe2x80x94 or xe2x80x94OSiR12Oxe2x80x94, and/or may optionally be substituted by methyl or ethyl,
n denotes the numbers 2, 3 or 4,
Q1, Q2 independently of one another denote a divalent radical,
A, P independently of one another denote a unit that can adsorb electromagnetic radiation,
with the proviso that the absorption maxima of the radicals xe2x80x94Q1xe2x80x94A and xe2x80x94Q2xe2x80x94P are at a distance of at least 200, preferably at least 500, and at most 10 000, preferably at most 9 000 cmxe2x88x921, from one another.
An essential feature of the invention is the recognition that the properties of the polymers according to the invention are better xe2x80x9cif terminal groups xe2x80x94Q1xe2x80x94A and xe2x80x94Q1xe2x80x94P are more similar to each other.xe2x80x9d This applies in particular with respect to their electronic configuration. The agreement of the orbital symmetry of both groups should be large, but not 100%. By exciting the longer wavelength adsorbing group in the first excited electronic (1S0) state, the orbital symmetries of the groups A and P become approximately anti-symmetrical.
The function of the radicals T1 and T2 is to ensure a specific spacing of the side-group ends from the chain acting as the backbone. They are therefore also termed xe2x80x9cspacersxe2x80x9d.
The radicals Q1 and Q2 join the terminal groups A and P to the spacers T1 and T2, which in turn form the bond to the main chain via the bonding member S1 and S2. The special feature of the groups Q1 and Q2 is their influence on both A and P on the one hand, as well as on T1 and T2 on the other hand. The radicals Q1 and Q2 are thus of quite special importance: for example, a similarity of the configuration, combined with a relatively similar position of the absorption maxima of xe2x80x94Q1xe2x80x94A and xe2x80x94Q2xe2x80x94P, are for example achieved if identical radicals A and P are differently strongly polarised by different radicals Q1 and Q2.
Preferred radicals Q1 and Q2 contain independently of one another the groups xe2x80x94Sxe2x80x94, xe2x80x94SO2, xe2x80x94Oxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CONR1xe2x80x94, xe2x80x94NR1COxe2x80x94, xe2x80x94NR1xe2x80x94,xe2x80x94(CH2)mxe2x80x94 where m=1 or 2, a divalent 6-membered ring with optionally 1 to 2 N atoms (in which case the coupling to the radicals T1 and A and to T2 and P takes place via these N atoms) and the group Z1xe2x80x94Xxe2x80x94Z2 wherein
Z1, Z2 independently of one another denote the groups xe2x80x94Sxe2x80x94, xe2x80x94SO2, xe2x80x94Oxe2x80x94, xe2x80x94COOxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94CONR1xe2x80x94, xe2x80x94NR1COxe2x80x94, xe2x80x94NR1xe2x80x94, xe2x80x94Nxe2x95x90Nxe2x80x94, xe2x80x94CHxe2x95x90CHxe2x80x94, xe2x80x94Nxe2x95x90CHxe2x80x94, xe2x80x94CHxe2x95x90Nxe2x80x94 or the group xe2x80x94(CH2)mxe2x80x94 where m=1 or 2, and
X denotes the naphthalene radical, a 5-membered or 6-membered cycloaliphatic, aromatic or heterocyclic ring, the group xe2x80x94(CHxe2x95x90CH)mxe2x80x94 where m=1 or 2, or a direct bond.
Particularly preferred radicals X include 2,6-naphthylene and 1,4-phenylene, and heterocyclic radicals of the structures 
If X denotes a 5-membered ring system this may for example be a carbocyclic or, preferably, a heteroaromatic system and may contain up to 3 hetero atoms, preferably from the series S, N, O. Suitable representatives are for example thiophene, thiazole, oxazole, triazole, oxadiazole and thiadiazol. Heterocycles with 2 hetero atoms are particularly preferred.
If X denotes the group xe2x80x94(CHxe2x95x90CH)mxe2x80x94, then m preferably has the value 1.
If X denotes a direct bond, the resultant compounds then are for example oxalic acid derivatives or urea derivatives, or carbamates (Z selected from Z1 and Z2).
The preferred meanings of Z1xe2x80x94Xxe2x80x94Z2 are benzoic acid amide radicals and benzoic acid ester radicals of the type xe2x80x94Oxe2x80x94C6H4xe2x80x94COOxe2x80x94, xe2x80x94Oxe2x80x94C6H4xe2x80x94COxe2x80x94NR1xe2x80x94, xe2x80x94NR1xe2x80x94C6H4xe2x80x94COOxe2x80x94, xe2x80x94NR1xe2x80x94C6H4xe2x80x94COxe2x80x94NR1xe2x80x94, as well as fumaric acid ester and fumaric acid amide radicals of the type xe2x80x94OCOxe2x80x94CHxe2x95x90CHxe2x80x94OCOxe2x80x94 and xe2x80x94NR1xe2x80x94COxe2x80x94CHxe2x95x90CHxe2x80x94COxe2x80x94NR1.
Q1 particularly preferably denotes the groups xe2x80x94Z1xe2x80x94C6H4xe2x80x94Nxe2x95x90Nxe2x80x94 and Q2 denotes the group xe2x80x94Z1xe2x80x94C6H4xe2x80x94COxe2x80x94NHxe2x80x94.
The groups xe2x80x94Q1xe2x80x94A should have absorption maxima in the wavelength range from 15000 to 28000 cmxe2x88x921, and the groups xe2x80x94Q2xe2x80x94P should have absorption maxima in the wavelength range from 16000 to 29000 cmxe2x88x921. For the purposes of the present invention A and P as well as Q1 and Q2 are defined so that the longer wavelength absorbing unit is termed xe2x80x94Q1xe2x80x94A, while the shorter wavelength adsorbing unit is termed xe2x80x94Q2xe2x80x94P.
Preferred radicals A and P include mononuclear and polynuclear radicals, for example cinnamic acid, biphenyl, stilbene and azo dye radicals, benzoic acid anilides or heterocyclic type analogues, preferably monoazo dye radicals.
Particularly preferred radicals A and P correspond to the formula
xe2x80x94Exe2x80x94N=Nxe2x80x94Gxe2x80x83xe2x80x83(III)
wherein
G denotes a monovalent aromatic or heterocyclic raadical and
E denotes a bivalent aromatic or heterocyclic radical.
In the case of E suitable aromatic radicals preferably contain 6 to 14 C atoms in the aromatic ring, which may be singly or multiply substituted by C1-C12 alkyl, C1-C12 alkoxy, hydroxy, halogen (in particular F, Cl, Br), amino, nitro, trifluoromethyl, cyano, carboxy, COOR (R=C1-C6 alkyl, cyclohexyl, benzyl, phenyl), C5-C12 cycloalkyl, C1-C12 alkylthio, C1-C6 alkylsulfonyl, C6-C12 arylsulfonyl, aminosulfonyl, C1-C6 alkylaminosulfonyl, phenylaminosulfonyl, aminocarbonyl, C1-C6 alkylaminocarbonyl, phenylaminocarbonyl, C1-C4 alkylamino, di-C1-C4 alkylamino, phenylamino, C1-C5 acylamino, C1-C4 alkylsulfonylamino, mono- or di-C1-C4 alkylaminocarbonylamino, C1-C4 alkoxycarbonylamino or trifluoromethylsulfonyl.
In the case of E suitable heterocyclic radicals preferably contain 5 to 14 ring atoms, of which 1 to 4 hetero atoms are from the series nitrogen, oxygen, sulfur, the heterocyclic ring system being able to be singly or multiply substituted by C1-C12 alkyl, C1-C12 alkoxy, hydroxy, halogen (in particular F, Cl, Br), amino, nitro, trifluoromethyl, cyano, carboxy, COOR (R=C1-C6 alkyl, cyclohexyl, benzyl, phenyl), C5-C12 cycloalkyl, C1-C12 alkylthio, C1-C6 alkylsulfonyl, C6-C12 arylsulfonyl, aminosulfonyl, C1-C6 alkylaminosulfonyl, phenylaminosulfonyl, aminocarbonyl, C1-C6 alkylaminocarbonyl, phenylaminocarbonyl, C1-C4 alkylamino, di-C1-C4 alkylamino, phenylamino, C1-C5 acylamino, C1-C4 alkylsulfonylamino, mono- or di-C1-C4 alkylaminocarbonylamino, C1-C4 alkoxycarbonylamino or trifluoromethylsulfonyl.
In the case of G suitable aromatic radicals preferably contain 6 to 14 C atoms in the aromatic ring, which may be singly or multiply substituted by C1-C12 alkyl, C1-C12 alkoxy, hydroxy, halogen (in particular F, Cl, Br), amino, nitro, trifluoromethyl, cyano, carboxy, COOR (R=C1-C6 alkyl, cyclohexyl, benzyl, phenyl), C5-C12 cycloalkyl, C1-C12alkylthio, C1-C6alkylsulfonyl, C6-C12 arylsulfonyl, aminosulfonyl, C1-C6 alkylaminosulfonyl, phenylaminosulfonyl, aminocarbonyl, C1-C6 alkylaminocarbonyl, phenylaminocarbonyl, C1-C4 alkylamino, di-C1-C4 alkylamino, phenylamino, C1-C5 acylamino, C6-C10 arylcarbonylamino, pyridylcarbonylamino, C1-C4 alkylsulfonylamino, C6-C12 arylsulfonylamino, mono or di-C1-C4 alkylaminocarbonyl-amino, C1-C4 alkoxycarbonylamino or trifluoromethylsulfonyl.
In the case of G suitable heterocyclic radicals preferably contain 5 to 14 ring atoms, of which 1 to 4 hetero atoms are from the series nitrogen, oxygen, sulfur, the heterocyclic ring system being able to be singly or multiply substituted by C1-C12 alkyl, C1-C12 alkoxy, hydroxy, halogen (in particular F, Cl, Br), amino, nitro, trifluoromethyl, cyano, carboxy, COOR (R=C1-C6 alkyl, cyclohexyl, benzyl, phenyl), C5-C12 cycloalkyl, C1-C12 alkylthio, C1-C6 alkylsulfonyl, C6-C12 arylsulfonyl, aminosulfonyl, C1-C6 alkylaminosulfonyl, phenylaminosulfonyl, aminocarbonyl, C1-C6 alkylaminocarbonyl, phenylaminocarbonyl, C1-C4 alkylamino, di-C1-C4 alkylamino, phenylamino, C1-C5 acylamino, C1-C4 alkylsulfonylamino, mono- or di-C1-C4 alkylaminocarbonylamino, C1-C4 alkoxycarbonylamino or trifluoromethylsulfonyl.
If the radicals E or G are multiply substituted, the number of substituents is governed in each case by the number of possible substitution positions, the possibility of incorporating the substituents, and the properties of the substituted systems. The aryl and acyl radicals may optionally be substituted by nitro, cyano, halogen, C1-C4 alkoxy or amino.
Particularly preferred radicals xe2x80x94Exe2x80x94Nxe2x95x90Nxe2x80x94G contain either an aromatic radical and a heterocyclic radical (i.e. either E or G are aromatic, the other radical being heterocyclic), or two aromatic radicals (i.e. both E and G are aromatic).
The preferred radicals xe2x80x94Exe2x80x94Nxe2x95x90Nxe2x80x94G are azobenzene radicals of the formula 
wherein
R denotes nitro, cyano, benzamido, p-chloro, p-cyano, p-nitrobenzamido or dimethylamino, and the rings A and B may additionally be substituted. Particularly preferred radicals A and P correspond go the formula 
wherein
R2 to R6 independently of one another denote hydrogen, chlorine, bromine, trifluoromethyl, methoxy, SO2CH3, SO2CF3, SO2NH2, N(CH3)2, preferably nitro, cyano or p-chloro, p-cyano, p-nitrobenzamido, with the proviso that at least one of these radicals is not hydrogen, and
R7 to R10 independently of one another denote hydrogen, chlorine or methyl.
In the case of multiple substitution of the ring A, the 2,4- and 3,4-positions are preferred.
Other preferred radicals A and P correspond to the formula: 
wherein
R2 to R6 and R7 to R10 have the aforementioned meanings, and
R2xe2x80x2 to R6xe2x80x2 have the same meanings as R2 to R6, although independently of the latter.
Other preferred radicals A and P correspond to the formula 
wherein
K, L, M independently of one another denote the atoms N, S, O or optionally xe2x80x94CH2xe2x80x94 or xe2x80x94CHxe2x95x90, with the proviso that at least one of the members K, L, M is a hetero atom and the ring A is saturated or contains 1 or 2 double bonds, and
R7 to R11 independently of one another have the meanings specified above for R7 to R10.
The ring A preferably denotes a thiophene, thiazole, oxazole, triazole, oxadiazole or thiadiazole radical.
Preferred radicals xe2x80x94Q1xe2x80x94A and xe2x80x94Q2xe2x80x94P correspond to the formulae 
wherein
R1 to R10 have the meanings specified above.
Preferred groups A and P correspond to the formulae 
wherein
R2 denotes hydrogen or cyano,
R2xe2x80x2 denotes hydrogen or methyl,
W denotes oxygen or NR1, and
R4 denotes nitro, cyano, benzamido, p-chloro, p-cyano, p-nitrobenzamido or dimethylamino.
Common to the above formulae is the fact that substitutions in the 4-, 2,4- and 3,4-positions of the ring A are particularly preferred.
For these preferred groups A and P, preferred groups xe2x80x94S1xe2x80x94T1xe2x80x94Q1xe2x80x94 and xe2x80x94S2xe2x80x94T2xe2x80x94Q2 xe2x80x94 correspond to the formulae xe2x80x94OCH2CH2Oxe2x80x94, xe2x80x94OCH2CH2OCH2CH2Oxe2x80x94 and xe2x80x94OCH2CH2NR1xe2x80x94.
The preferred polymers according to the invention contain only repeating units with the side groups I and II, and more particularly preferably those of the formulae 
where R=H or, preferably, methyl.
The corresponding preferred monomers for introducing the side groups I and II thus correspond to the formulae 
The side groups (I) and (II) are thus preferably joined to (meth)acryloyl groups CH2xe2x95x90C(R)xe2x80x94COxe2x80x94 where R=hydrogen or methyl.
Preferably the main chain of the side-group polymers is formed from monomers that carry the side groups (I), from monomers that carry the side group (II), and optionally from further monomers, in which connection in particular the proportion of the monomers that exhibit the side group (I) is 10 to 95 mole %, preferably 20 to 70 mole %, the proportion of the monomers that exhibit the side group (II) is 5 to 90 mole %, preferably 30 to 80 mole %, and the proportion of the further monomers is 0 to 50 mole %, in each case referred to the sum of all incorporated monomer units.
As xe2x80x9cfurtherxe2x80x9d repeating units, all basic building blocks which can be incorporated chemically into the side-group polymer are suitable. They substantially serve simply to reduce the concentration of the side groups I and II in the polymer and thus produce, as it were, a xe2x80x9cdilutionxe2x80x9d effect. In the case of poly(meth)acrylates the xe2x80x9cfurtherxe2x80x9d monomer include ethylenically unsaturated copolymerisable monomers that preferably carry xcex1-substituted vinyl groups or xcex2-substituted alkyl groups, preferably styrene; however, also suitable are for example nuclear-chlorinated and alkylated or alkenylated styrenes, the alkyl groups being able to contain 1 to 4 carbon atoms and the alkenyl groups being able to contain 2 to 4 carbon atoms, for example vinyl toluene, divinyl benzene, xcex1-methyl styrene, tert.-butyl styrenes, chlorinated styrenes; vinyl esters or carboxylic acids with 2 to 6 carbon atoms, preferably vinyl acetate, vinyl pyridine, vinyl naphthalene, vinyl cyclohexane, acrylic acid and methacrylic acid and/or their esters (preferably vinyl, allyl and methallyl esters) with 1 to 4 carbon atoms in the alcohol component, their amides and nitrites, maleic anhydride, maleic acid semi-esters and dyesters with 1 to 4 carbon atoms in the alcohol component, maleic acid semi-amides and diamides and cyclic imides such as N-methyl maleimide or N-cyclohexyl maleimide, allyl compounds such as allyl benzene and allyl esters such as allyl acetate, phthalic acid diallyl esters, isophthalic acid diallyl esters, fumaric acid diallyl esters, allyl carbonates, diallyl carbonates, triallyl phosphate and triallyl cyanurate.
Preferred xe2x80x9cfurtherxe2x80x9d monomers correspond to the formula 
wherein
R12 denotes an optionally branched C1-C6 alkyl radical or a radical containing at least one further acrylic radical.
The polymers according to the invention may also contain more than one side group that falls under the definition of (I), or more than one side group that falls under the definition of (IIa) and (IIb), or several side groups that fall under the definition of both (I) and (IIa) and (IIb).
The polymers according to the invention preferably have glass transition temperatures Tg of at least 40xc2x0 C. The glass transition temperature may be determined for example according to B. Vollmer, Grundrixcex2 der Makromolekularen Chemie (Foundations of Macromolecular Chemistry), pp. 406 to 410, Springer-Verlag, Heidelberg 1962).
The polymers according to the invention generally have a weight average molecular weight of 3000 to 2000000, preferably 5000 to 1500000, as determined by gel permeation chromatography (calibrated with polystyrene).
Structural elements with a high dimensional anisotropy and high molecular polarisability anisotropy are the prerequisite for high values of the optical anisotropy. By means of the structure of the polymers the intermolecular interactions of the structural elements (I) and (IIa) and (IIb) are adjusted so that the formation of liquid crystal order states is suppressed, and optically isotropic, transparent non-scattering films can be produced. On the other hand the intermolecular interactions must nevertheless be strong enough so that, on irradiation with polarised light, a photochemically induced, co-operative, directed re-orientation process of the side groups is effected.
In the optically isotropic, amorphous polymers according to the invention extremely high values of the optical anisotropy can be induced by irradiation with polarised light. The measured values of the change in double refraction xcex94n are between 0.05 and 0.8.
As light there is preferably used linearly polarised light whose wavelength lies in the range of the absorption bands of the side groups.
The present invention also provides polymers in which double refraction changes xcex94n of more than 0.15, preferably more than 0.2, and in particular more than 0.4, can be inscribed using polarised light. The value xcex94n should be measured as described hereinafter:
First of all in each case the absorption maxima xcexmax1 and xcexmax2 are measured in both homopolymers. A double refraction change is produced by irradiating a film of the copolymer to be tested using linearly polarised light of a wavelength of (xcexmax1+xcexmax2):2. For this purpose the samples are irradiated with polarised light in the direction of the normal to the surface. The output of the light source should be 1000 mW/cm2; in the case that the copolymer is destroyed under these conditions, the output of the light source is reduced in 100 mW steps until the copolymer is no longer destroyed by the irradiation. The irradiation is continued until the double refraction no longer changes. The double refraction change that is produced is measured with a selective wavelength of [(xcexmax1+xcexmax2):2]+350xc2x150 [nm]. The polarisation of the measuring light should form an angle of 45xc2x0 relative to the direction of polarisation of the inscribing light.
The preparation of the side-group monomers and their polymerisation can be carried out according to processes known in the literature; see for example Makromolekulare Chemie 187, 1327-1334 (1984), SU 887 574, Europ. Polym. 18, 561 (1982) and Liq. Cryst. 2, 195 (1987), DD 276 297, DE-OS 28 31 909 and 38 08 430. The polymers according to the invention are generally prepared by free-radical copolymerisation of the monomers in suitable solvents, for example aromatic hydrocarbons such as toluene or xylene, aromatic halogenated hydrocarbons such as chlorobenzene, ethers such as tetrahydrofuran or dioxane, ketones such as acetone or cyclohexanone, and/or dimethyl formamide in the presence of radical-donating polymerisation initiators, for example azobis(isobutyronitrile) or benzoyl peroxide, at elevated temperatures, generally at 30 to 130xc2x0 C., preferably at 40 to 70xc2x0 C., with exclusion of water and air as far as possible. Isolation can be carried out by precipitation with suitable agents, for example methanol. The products can be purified by re-precipitation, for example with chloroform/methanol.
The present invention thus also provides a process for preparing the side-group polymers by copolymerisation of the corresponding monomers.
The polymers are processed into layers whose thickness is 0.1 to 500 xcexcm, preferably 1 to 30 xcexcm, particularly preferably 2 to 10 xcexcm. They can be cast from solution, applied with a knife, dipped, or spin coated. They can form self-supporting films. Preferably however they are applied to supporting materials. This can be effected by various techniques known per se, the process being selected according to whether a thick or thin layer is desired. Thin layers may be produced for example by spin coating or knife application from solutions or the melt, while thicker layers may be produced by melt pressing or extrusion.
It is possible successfully to produce isotropic films without the need for time-consuming and costly orientation processes using external fields and/or surface effects. The films can be applied to substrates by spin coating, immersion, casting or other technologically easily controllable coating processes, introduced between two transparent plates by pressing or inflow, or can simply be produced as self-supporting films by casting or extrusion. Such films can also be produced from liquid-crystal polymers that contain the structural elements in the aforedescribed sense, by sudden cooling, i.e. at a cooling rate of greater than 100 K/min, or by rapidly draining off the solvent.
The invention therefore also provides films (both self-supporting and in the form of coatings) formed from the aforedescribed polymers, as well as supports coated with these films.
The side-group polymers according to the invention are optically isotropic, amorphous, transparent and non-light-scattering in the glassy state of the polymers and can form self-supporting films.
Preferably however they are applied to supporting materials, for example glass or plastics films. This can be effected by various techniques known per se, the particular process being chosen according to whether a thick or thin film is desired. Thin films can be produced for example by spin coating or knife application from solutions or from the melt, while thicker films can be produced by filling preprepared cells, or by melt pressing or extrusion.
The polymers can be used for digital or analog data storage in the widest sense, for example for optical signal processing, for Fourier transforms and folding or in coherent optical correlation techniques. The lateral resolution is limited by the wavelength of the inscribing light, and permits a pixel size of 0.45 to 3000 xcexcm, preferably a pixel size of 0.5 to 30 xcexcm.
This property makes the polymers particularly suitable for processing images and for information processing by means of holograms, which can be reproduced by illuminating with a reference beam. Similarly, the interference pattern can store two monochromatic coherent light sources with constant phase relation. Accordingly, three-dimensional holographic images can be stored. The images are read by illuminating the hologram with monochromatic, coherent light. On account of the relationship between the electrical vector of the light and the associated preferred direction in the storage medium, a higher storage density can be achieved than with a purely binary system. With analog storage values of the grey scale can be adjusted continuously and locally resolved. Information that is stored in an analog manner can be read in polarised light, and the positive or the negative image can be created depending on the position of the polarisers. In this connection the contrast of the film produced by the phase displacement of the ordinary and extraordinary beam between two polarisers can be utilised, the planes of the polariser advantageously forming an angle of 45xc2x0 relative to the plane of polarisation of the inscribing light, and the plane of polarisation of the analyser being either at right angles or parallel to that of the polariser. Another possibility is to detect the angle of deflection of the reading light produced by induced double refraction.
The polymers can be used as optical components that can be passive or can be actively switched, in particular for holographic optics. The high light-induced optical anisotropy can thus be used for the electrical modulation of the intensity and/or polarisation state of light. Accordingly, components can be produced from a polymer film by holographic structuring that have image-forming properties comparable to lenses or gratings.
The layers can be used for the serial recording of light-transmitting data of all types, especially of images in the medical sector.
The invention therefore also provides for the use of the optically anisotropic substrates in information technology, especially as structural elements and components for storing and processing information, preferably images, and as holographic recording material.
The percentage figures in the following examples refer, unless otherwise stated, in each case to parts by weight.